Computer system

ABSTRACT

In a distributed file system, when a user requests a computer to create a distributed file, a management computer acquires a list of computers complying with an allocation rule selected by the user from allocation rules taking the performance, security level, reliability level and utility rate into consideration. When the user requests the computer to access the distributed file, on the other hand, the partial files and the server information are collected from each computer. Each computer evaluates the allocation of the partial files based on the selected allocation rule and the server information from each computer, and if required, selects a destination computer and instructs the partial files to be moved to the destination computer.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a computer system comprising aplurality of computers connected to each other through a network, or inparticular to a distributed file system for managing filesdistributively for the computer system.

A conventional distributed file system for a computer system isdisclosed in JP-A-8-77054 as a specific example of the technology inwhich a cluster of data (hereinafter referred to as “file”) used bycomputer programs, etc. is divided into a plurality of portions(hereinafter referred to as “partial files”) arranged distributivelyamong a plurality of computers.

On the other hand, JP-A-2000-207370 discloses a file distributionmethod, in which partial files are arranged among a plurality ofcomputers based on the load information shared by the computers,including the load of each computer such as the maximum data transferrate of each computer and the occupancy rate of the storage unit of eachcomputer. Also, according to the method disclosed by JP-A-2000-207370,in the case where a heavy load is imposed on a given computer, thepartial files stored in the heavily loaded computer is transferred toother computers.

Also, a distributed file system for a wide-area network based on theassumption that more than hundreds of thousands of computers areconnected is proposed in the Sean Rhea et al paper entitled“Maintenance-Free Global Data Storage” (IEEE Internet Computing, Vol. 5,No. 5, September/October 2001, pp. 40-49). In the distributed filesystem described by this reference, the positions of partial filescannot be specified from a given partial file due to the difference insecurity level or reliability between the computers connected to thewide-area network. In this way, the security of the distributed filesystem can be maintained.

In the distributed file system disclosed in JP-A-2000-207370, partialfiles are moved based only on the load information. In the case where acomputer higher in performance than other computers exists in a system,therefore, all the partial files making up a single file may betransferred to the same computer. In such a case, the distribution ofpartial files making up a given file is meaningless. This disadvantagecan be obviated by confirming whether the destination of a partial filehas another partial file making up the same file. Specifically, theposition of a given partial file making up the same file is specifiedfrom the information on another partial file. According to this method,however, as disclosed in the Sean Rhea et al reference above, thesecurity is not maintained for the distributed file system.

Also, in the conventional distributed file system, only the loadinformation of each computer is taken into consideration when layingdown the rules (hereinafter referred to as “allocation rule”) fordetermining the allocation of the partial files or moving the partialfiles. In the distributed file system according to the prior art,therefore, the partial files cannot be arranged or moved under theallocation rules stipulated taking into consideration the difference, ifany, in performance, security, reliability level or utility rate betweenthe computers.

Further, in the distributed file system disclosed in JP-A-8-77054,JP-A-2000-207370 and the Sean Rhea et al reference cited above, noconsideration is given to the concept of laying down a plurality ofallocation rules based on a plurality of types of information and usingthem differently from each other depending on the situation.

SUMMARY OF THE INVENTION

An object of this invention is to provide a distributed file managementmethod and a distributed file system using the same method, in whichsecurity is maintained while at the same time solving the problem thatall partial files moved are concentrated in a single computer.

Another object of the invention is to provide a file management methodand a distributed file system using the same method for a computersystem in which partial files are arranged according to variousallocation rules.

In order to achieve the objects described above, according to one aspectof this invention, there is provided a computer system comprising aplurality of computers (hereinafter referred to as “the computer l”)having a storage unit for storing data, a computer (hereinafter referredto as “the computer 2”) of the user and a computer (hereinafter referredto as “the management computer”) for managing the aforementionedcomputers, these computers being connected by a network. In thiscomputer system, the computers 1 manage the performance, security level,reliability level, the utility rate, load information, etc. thereof andtransmits these information to the management computer. The managementcomputer collectively manages these information transmitted. On theother hand, the computer 2 has information or allocation rules includinga plurality of items for defining the distribution of the partial filesmaking up a file.

When user instructs the computer 2 to create files to be distributed,the computer 2 transmits the information on the allocation rules to themanagement computer in order to acquire information on the computers 1meeting the allocation rules. The management computer that has receivedthe allocation rules accesses the information of each computer 1 managedby itself, specifies the computer 1 to which the received allocationrules are applicable, and transmits the information on the specifiedcomputer 1 to the computer 2.

The computer 2 that has received the information on the computer 1 towhich the allocation rules are applicable transmits, based on theparticular information, the partial files of the file to each computer 1complying with the allocation rules.

According to another aspect of the invention, the computer system may beso configured that the partial files are relocated with a specifiedevent as a motive.

At such a specific event, the computer 2 receives the information on agiven computer 1 from the particular computer 1 having partial filesmaking up a file to be relocated. The computer 2 that has received theinformation on the computer 1 compares the allocation rules of thecomputer 2 with the received information on the computer 1, and confirmsthe presence or absence of a computer 1 failing to comply with theallocation rules at the particular time point.

In the presence of a computer 1 failing to comply with the allocationrules, the computer 2 transmits the information on the allocation rulesto the management computer in order to confirm the computers 1 complyingwith the allocation rules. The management computer that has received theallocation rules accesses the information on the computers 1 managed byitself, and specifying the computers 1 complying with the receivedallocation rules, transmits the information on the particular computers1 to the computer 2.

The computer 2 that has received the information on the computers 1complying with the allocation rules selects a specified computer 1 fromthe received information on the computers 1. After that, the computer 2transmits an instruction to the computers 1 failing to comply with theallocation rules to transfer the partial files to the specifiedcomputers 1 complying with the allocation rules.

The computers 1 and the computer 2 may double as a management computer,and the computer 1 can double as the computer 2.

According to still another aspect of the invention, the priority of theitems making up the allocation rules of the computer 2 may be set. Inthe absence of the computers 1 complying with the allocation rules, thecomputer 2 relaxes the allocation rules and secures a computer 1 makingup the destination of the file (object of relocation) by eliminating theitems of low priority from the allocation rules. Any item with priorityof zero is not considered to constitute the contents of the allocationrules.

According to yet another aspect of the invention, the computer 2 has aplurality of allocation rules, and uses different allocation rules fordifferent types of files distributed. Also, at the time of filedistribution, the user may select or set the priority of each item ofthe allocation rules so that the files are distributed according to theresult of the selection or setting, as the case may be.

When the computers 1 complying with the allocation rules are notsufficient in number, the computer 2 may store a plurality of partialfiles in a single computer 1.

According to a further aspect of the invention, the movement of thepartial files is withheld until predetermined conditions are met for thecomputer 1 instructed to move the partial files. In this case, thecomputer 1 receives a plurality of move instructions for each partialfile. The computer 1 checks to see whether some prospective destinationcomputers 1 included in the plurality of the move instructions aredoubled or not, and only in the presence of a double computer 1, thepartial files are transferred. The predetermined conditions are definedto include a predetermined time length or the time length beforereceiving a predetermined number of instructions.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a computer system according to anembodiment of this invention.

FIG. 2 is a diagram showing an example of a distributed file informationmanagement table.

FIG. 3 is a diagram showing an example of a server informationmanagement table.

FIG. 4 is a diagram showing an example of allocation rules and prioritysetting information.

FIG. 5 is a flowchart showing an example of the processing operation forselecting a destination computer for partial files.

FIG. 6 shows an example of the allocation rules and the priority settinginformation.

FIG. 7 is a flowchart showing an example of the processing operation forselecting a destination computer of partial files.

FIG. 8 shows an example of the allocation rules and the priority settinginformation.

FIG. 9 shows an example of a correspondence table showing the applicablerules for different types of distributed files.

FIG. 10 is a diagram showing an example of a distributed fileinformation management table.

FIG. 11 is a diagram showing an example of a configuration of acomputer.

FIG. 12 is a diagram showing an example of a partial file informationmanagement table.

FIG. 13 is a diagram showing an example of the file attributeinformation of the partial file information management table.

FIG. 14 is a diagram showing an example of a table for registering theinformation as to the advisability of copying the partial files.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of this invention will be explained in detail below withreference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a computer systemaccording to an embodiment of the invention. The computer system shownin FIG. 1 comprises computers 1A, 1B, 1C, 2A, 2B and a managementcomputer 4, all of which are interconnected by a network 3.

FIG. 11 is a diagram showing an example of a configuration of thecomputer 1. The computer 1 comprises a storage unit 14 such as a harddisk or a disk array for storing data such as files and partial filesand a control unit 15. The control unit 15 includes a processor 16, amemory 17, an interface 18 and a network interface 19. The processor 16executes a program such as an operating system for managing the partialfiles and the files stored in the storage unit 14. These programs arestored in the memory 17, and installed in the computer 1 through aportable storage medium such as a floppy disk (registered trade name) ora network.

The storage unit 14 may be either integrated with the control unit 15 inthe same housing or built in another housing. The control unit 15 andthe storage unit 14 are connected to each other through the interface 18such as SCSI or fiber channel. The control unit 15 and the storage unit14, if accommodated in different casings, may be connected to each otherby a storage area network constructed of fiber channels or the like.When the control unit 15 and the storage unit 14 are accommodated indifferent housings, the storage unit 14 may further have a control unitfor controlling the storage unit 14 in its entirety.

The memory 17 has stored therein a server status management program 11,a partial file management program 12 and a partial file relocationprogram 13.

The server status management program 11 is executed in the case wherethe information such as the performance, security level, reliabilitylevel, utility rate or load for the computer 1 (hereinafter referred toas “the server information”) is managed by the control unit 15. In thecase where the server information is changed, the control unit 15executes the program 11 and notifies the contents of change to themanagement computer 4 through the network 3. According to thisembodiment, the control unit 15 notifies the management computer 4 ofonly the change of the server information not frequently updated (suchas the performance, security level, reliability level and utility rate).

The control unit 15 transmits the server information of the computer 1itself to the computer 2 based on the result of execution of the partialfile management program 12.

The partial file management program 12 is executed in the case where thepartial files stored in the storage unit 14 of the computer 1 aremanaged by the control unit 15. This program is executed also in thecase where the partial files are written, read or transmitted to therequester computer 2 by the control unit 15 in response to a requestfrom the computer 2.

The partial file relocation program 13 is executed in the case where thecontrol unit 15 determines the destination of a partial file or controlsthe transfer of the partial file to other computers 1 in compliance withan instruction of the computer 2 to move the partial file. The program13 is executed also in the case where the control unit 15 that hasreceived a request of the control unit 15 of another computer 1 toreceive a partial file receives the requested partial file and stores itin the storage unit 14.

The management computer 4 has a similar configuration to the computer 1and includes a processor, a memory, an input/output unit and a storageunit. The memory has stored therein a distributed file informationmanagement table 43, a server information management table 44, adistributed file management program 41 and a server informationmanagement program 42.

The distributed file management program 41 is executed in the case wherethe position of each partial file making up the file manageddistributively (hereinafter referred to as “the distributed file”) ismanaged by the management computer 4. Based on the notification forcreating a distributed file from the computer 2, the management computer4 determines an ID (hereinafter referred to as “the partial file ID”)unique to each partial file making up the notified distributed file, andmanages the distributed file name, the partial file ID and the name ofthe computer storing each partial file as related to each other. Adistributed file information management table 43 is used for thismanagement. The contents of this table 43 will be described later.

The program 41 is executed also in the case where the partial file IDsand a list of the partial file positions are transmitted to the computer2 in response to an inquiry from the computer 2 about the IDs andpositions of the partial files making up the distributed file.

The server information management program 42 is executed in the casewhere the management computer 4 manages the server informationtransmitted from the control unit 15 of each computer 1. A serverinformation management table 44 is used for management of the serverinformation. The contents of this table 44 will be described later. Theprogram 42 is executed also in the case where the management computer 4searches the server information management table 44 for the computer 1complying with the allocation rules contained in the inquiry from thecomputer 2 in response to the same inquiry and returns the result to thecomputer 2.

The computer 1 may have a distributed file management program 41 andthus can double as the management computer 4.

The computer 2 has a similar configuration to the computer 1, andcomprises a processor, a memory, an input/output unit and a storageunit. The computer 2 receives a user instruction through theinput/output unit. The computer 1 or the management computer 4 may havean input/output unit for receiving the user instruction and thus maydouble as the computer 2. The memory has stored therein allocation rules23, a distributed file operating program 22 and a partial fileallocation evaluation program 21.

The distributed file operating program 22 is executed in the case wherea distributed file is divided into partial files, a destination computer1 is confirmed and a partial file creation request is transmitted toeach computer 1 in response to a distributed file creation request fromthe user.

The partial file allocation evaluation program 21 is executed in thecase where an inquiry is made to the management computer 4 by thecomputer 2 about the presence or absence of the computer 1 complyingwith the allocation rules based on the items including the performance,security level, reliability level, utility rate and load information setin the computer 2 when the computer 2 confirms the computer 1 making upthe destination of the partial files. In the case where the number ofthe computers 1 complying with the allocation rules obtained as theresult of the inquiry is less than the number of partial files to bearranged, on the other hand, the computer 2 removes the items lowest inpriority from the allocation rules by executing the program 21 and makesan inquiry to the management computer 4 again about the presence orabsence of the computer 1 complying with the allocation-rules withoutthe particular items lowest in priority.

The computer 2 also checks the server information received from thecomputers 1 to see whether the computers 1 comply with the allocationrules stipulated in advance. In the case where the check shows that anyof the computers 1 fails to comply with the allocation rules, thecomputer 2 determines the computer 1 making up the destination of thepartial files stored in the computer 1 failing to comply with theallocation rules.

Specifically, the computer 2 makes an inquiry to the management computer4 about the presence or absence of the computer 1 complying with theallocation rule. In response to the request from the computer 2, themanagement computer 4 searches for the computer 1 complying with therequest and transmits the result to the computer 2. The computer 2determines computer 1 making up a destination among the computers 1satisfying the rule which have been received as the result from thecomputer 4 by excluding those computers 1 in which partial files havealready been allocated.

FIG. 1 illustrates the status after the creation of distributed files A,B, C. The partial file A1 (141) of the distributed file A is stored inthe storage unit 14 of the computer 1A, the partial file A2 (51) of thedistributed file A and the partial file B1 (52) of the distributed fileB are stored in the storage unit 14 of the computer 1B, and the partialfile B2 (61) of the distributed file B and the partial file C1 (62) ofthe distributed file C are stored in the storage unit 14 of the computer1C.

FIG. 2 illustrates an example of a distributed file informationmanagement table 43 held by the management computer 4 in the state shownin FIG. 1. The management computer 4 manages, using the table 43, thecorrespondence between the unique partial file ID attached to eachpartial file of each distributed file and the position where the partialfile is stored. In the case where each distribution file has attributeinformation, the particular attribute information is managed as an itemcorresponding to each partial file. In FIG. 2, the type of thedistributed file is managed as an example of the attribute informationof the distributed file. The other attribute information of thedistributed file are considered to include the file owner, the filecreation time and the file update time. These information aretransmitted to the management computer 4 by each computer 2 upon receiptof a distributed file creation request from the user.

FIG. 3 shows an example of the server information management table 44managed by the management computer 4. According to this embodiment, eachcomputer 1 manages the server information including the data transferrate (M bytes/s) of the storage unit 14 in terms of performance, thelevel of the user, etc. set by the manager of each computer 1 in termsof security level, the level set by the manager of each computer 1 interms of reliability level, the charge (yen/M bytes) corresponding tothe consumed capacity of the storage unit 14 of each computer 1 in termsof utility rate and the occupancy rate (%) of the storage area of thestorage unit 14 of each computer 1 in terms of load information. Onlythe information on performance, security level, reliability level andutility rate of which the value is rarely updated are assumed to betransmitted from each computer 1 to the management computer 4. This isin order to suppress the communication traffic between the managementcomputer 4 and each computer 1. As shown in FIG. 3, therefore, themanagement computer 4 manages only the information from each computer 1by means of the server information management table 44.

The server information may be registered in the management computer 4 insuch a manner that the server information is either transmittedautomatically to the management computer 4 from each computer 1connected through the network 3 or set manually by the user or themanager at the time of initial setting of the distributed file system.Each time of a change which the server information may undergo, on theother hand, the information is transferred from the computer 1 to themanagement computer 4 or manually registered by the user, etc.

FIG. 4 shows an example of an allocation rule table 23 defined inadvance in the computer 2A. In FIG. 4, performance, security,reliability, utility rate and load are employed as items of theallocation rules. Nevertheless, other combinations of the items may beused with equal effect.

In the allocation rule table 23, the priority is set for each item. Inthe case where the computers 1 complying with the allocation rules arenot sufficient in number, the computer 2 removes the items from theallocation rule table 23 in accordance with the priority set for eachitem and thus relaxes the conditions for the allocation rules. As aresult, the partial files can be distributed under the second-bestallocation rules.

In FIG. 4, performance is set as an item of 3 in priority, so that thepartial files are arranged for the computer 1 with the performance valueof not less than 40 (M bytes/s). On the other hand, security is set asan item of 1 in priority, so that the partial files are arranged in thecomputer 1 having a security level of not less than 4. Similarly,reliability is set as an item of 2 priority, so that the partial filesare arranged in the computer 1 having a reliability level of not lessthan 2. Further, utility rate and load are set as 0 in priority, therebyindicating that these are not applicable as items under the allocationrules. The description that follows assumes that the priority of 1 ishigher in priority than the priority of 3.

This embodiment deals with a case in which a single combination of itemsis set for the allocation rules. As other embodiments, however, theinvention is applicable to a case in which the user determines the orderof priority of items at the time of arranging each distributed file,thereby using allocation rules configured of items desired by the userat the time of arranging each distributed file.

In this case, the computer 2 displays the items of the allocation ruleson the input/output unit at the time of creating a distributed file, andcauses the user to input the order of priority of the items. In theprocess, the user sets a high priority for the desired items.Conversely, the user can eliminate a given item from the allocationrules by inputting the priority of 0 for the particular item. Further,the user may add a new item.

The items and the priority set in this way are recorded by the computer2 in a memory as an allocation rule table 23 for the distributed files.At the same time, the information on the set allocation rules istransmitted to the management computer 4. The management computer 4expands the distributed file information management table 43 of FIG. 2in the manner shown in FIG. 10, and manages the allocation rules foreach distributed file as attribute information of the distributed file.

According to this embodiment, the same allocation rules are used for alltypes of distributed files. In other embodiments, however, differentapplicable rules may be selected and the priority thereof setautomatically for different types of distributed files. In such a case,the computer 2, as shown in FIG. 9, holds different allocation ruletables 23 shown in FIG. 4 for different file types. At the request ofthe user to a create distributed file, the computer 2 automaticallyselects applicable allocation rules from the allocation rule table ofFIG. 9 in accordance with the file type required, and sets the priority,if necessary.

The information on the allocation rules for each file type set in thecomputer 2 may be either manually input by the user of the computer 1 orautomatically transferred from the management computer 4 when thecomputer 2 is newly connected to the network 3. Further, the informationon the newly added items for the allocation rules are transferred toeach computer 1 and the management computer 4, which start to collect orotherwise handle the server information corresponding to the added itemsof the allocation rules.

Next, an explanation will be given about the processing steps followedin the case where the user requests the computer 2A to create thedistributed file A whereby the partial file A1 (141) and the partialfile A2 (51) are created in the computer system shown in FIG. 1.

Upon receipt of a request from the user to create the distributed file Athrough the input/output unit, the computer 2A regards the filedesignated by the user as the distributed file A, and by dividing thedistributed file A into predetermined sizes, creates partial files (twopartial files A1 (141) and A2 (51) in this case). After that, thecomputer 2A notifies the management computer 4 of the number (two in thecase under consideration) of partial files to be created.

The management computer 4 creates as many unique partial file IDs as thepartial files notified from the computer 2A in the computer systemmanaged thereby, and notifies the computer 2A of the partial file IDsthus created. The computer 2A that has received the partial file IDsfrom the management computer 4 assigns the received partial file IDs toeach partial file. Further, the computer 2A determines the computers 1in which the partial files are to be arranged. The steps of thisdetermining process will be explained below.

FIG. 5 is a flowchart showing the steps followed by the computer 2A toestablish a list of the computers 1 in which the partial files are to bearranged.

First, the computer 2A selects all the items set to the priority of 1 orhigher, from the items of the allocation rule table 23 held therein. Inthe case where a specific allocation rule table 23 is predetermined foreach file, the computer 2 selects the particular specific allocationrule table 23 before selecting items (step 500). After that, thecomputer 2A transmits to the management computer 4 a command to make aninquiry about the computers 1 complying with the allocation rulesdefined by the selected items (step 501). The information on the itemsnot registered in the management computer 4, however, is not taken intoconsideration in the response from the management computer 4.

The computer 2A that has received the response to the inquiry command(step 509) determines whether “load” has been selected as an item of theallocation rules. This is by reason of the fact that according to thisembodiment, the “load” information is not managed by the managementcomputer 4, and therefore, it is necessary to determine again whetherthe conditions for “load” are met or not by a list of the computers 1transmitted from the management computer 4. Apart from “load” taken asan example of an item in this embodiment, items not managed by themanagement computer may be an item other than “load”. In the presence ofsuch an item, the computer 2 executes a similar process to the onedescribed herein for the particular item (step 502).

In the case where “load” is selected as an item, the computer 2A issuesa command to make inquiry about the current “load” information to allthe computers 1 included in the list of the computers 1 obtained in step501. Based on the response to the command, the computer 2A removes fromthe list the computers 1 failing to meet the conditions set for the item“load” of the allocation rules (step 503).

Next, the computer 2A determines whether the computers 1 not smaller innumber than the created partial files (2 in our case) are included inthe list of the computers 1 corrected in step 503 (step 504). In thecase where the computers 1 not less than the partial files are containedin the list, however, the computer 2 determines applicable allocationrules and the list of the computers 1 (step 507).

In the case where the number of computers 1 included in the list of thecomputers 1 is not more than the number of the partial files in step504, the computer 2A removes those items selected in step 501 for theallocation rules which are lowest in priority (step 505). Then, thecomputer 2A determines whether the items highest in priority, i.e. theitems of 1 in priority remain or not in the allocation rule table 23(step 506). In the case where no item of 1 in priority remains (all theitems have been removed), the computer 2A displays an alarm to the userwhile at the same time displaying the immediately preceding list (thelist of the computers 1 from which the items of 1 in priority are notyet removed) (step 508). In the case where the items of 1 in priorityremain in the allocation rule table 23 in step 506, the computer 2Arepeats the process of step 501 and subsequent steps, and thusestablishes a list of the computers 1 complying with the allocationrules made up of the remaining items.

After that, the computer 2A selects as many computers 1 as the partialfiles at random from the established list of the computers 1. Then, thecomputer 2A instructs each of the computers 1 thus selected (thecomputers 1A and 1B in the case under consideration) to create thepartial files A1 and A2, respectively. This instruction contains thedata on the partial files and the partial file IDs. Further, thecomputer 2A notifies the management computer 4 of the information on thedistributed file created, i.e. the distributed file name, the partialfile IDs and the places where the partial files are arranged(information specifying the computer 1).

As described above, the computer 2A issues an alarm to the user to theeffect that the computers 1 complying with the allocation rules are notsufficient in number, based on the process of step 508 shown in FIG. 5.At the same time, in the case where at least one computer 1 is includedin the created list of computers 1, the computer 2A may cause the userto determine whether all or a plurality of the partial files arearranged in the same computer 1. In the case where the user determinesthat all or a plurality of the partial files may be so arranged, thecomputer 2 arranges a plurality of the partial files in the samecomputer 1.

In the case where the list of the computers 1 complying with theallocation rules, except for the items low in priority, cannot beobtained based on the process of step 508 shown in FIG. 5, the computer2A may issue an alarm by displaying the removed items to the userthrough the input/output unit.

Next, the steps of operation of the computers 1 that have received theinstruction to create the partial files will be explained.

All the computers 1 (the computers 1A and 1B in the case underconsideration) instructed to create a partial file create the partialfiles in the internal storage unit 14 of the corresponding computer 1,respectively, based on the data transferred thereto together with theinstruction. Also, the computers 1 create a table of correspondencebetween the partial file IDs received from the computer 2A and thestorage positions of the partial files in the storage unit 14.

The management computer 4 that has received the inquiry command from thecomputer 2A in step 501 shown in FIG. 5 operates in the manner describedbelow. Specifically, based on the items of the allocation rulestransmitted from the computer 2A (FIG. 4), the management computer 4extracts the computers 1 (the computers 1A and 1B in the case underconsideration) complying with the allocation rules of FIG. 4 from theserver information management table 44 shown in FIG. 3. The informationon the computers 1 thus extracted is transmitted to the computer 2A as alist of the computers 1 complying with the allocation rules.

Next, an explanation will be given about the process of steps executedin the case where the user issues a request to the computer 2B to accessthe distributed file B and the process of the operation performed in thecase where the partial files are moved (relocated) with this accessrequest as a motive. Other motives for movement (relocation) of thepartial files may include the receipt by the computer 2 of a request torewrite the contents of the partial files, a predetermined period, or atime point designated by the user. Also, this embodiment assumes thatthe items of the allocation rules and the priority thereof are set inthe computer 2B as shown in FIG. 6.

First, assume that a request to access the distributed file B is givento the computer 2B from the user through the input/output unit. Thecomputer 2B transmits to the management computer 4 a command makinginquiry in which computer 1 each partial file making up the distributedfile B is located.

The management computer 4 that has received the inquiry command accessesthe distributed file information management table 43 and transmits tothe computer 2B the partial file IDs of the partial files of thedistributed file B and the names of the computers 1 storing theparticular partial files. According to this embodiment, the managementcomputer 4 transmits the information indicating that the partial file B1(52) and the partial file B2 (61) are stored in the computer 1B and thecomputer 1C, respectively.

The computer 2B that has received the information on the partial filesof the distributed file B from the management computer 4 transmits arequest to read the partial file B1 (52) to the computer 1B and arequest to read the partial file B2 (61) to the computer 1C. Eachcomputer 1 reads the corresponding partial file in response to therequest from the computer 2B and transmits it to the computer 2B. In theprocess, each computer 1 also transmits the server information of eachcomputer 1 to the computer 2B. In this embodiment, assume that theserver information shown in FIG. 8 is transmitted to the computer 2B. Inthe case where the files are relocated with another event as a motive,the computer 2 may issue a command to request the server informationfrom each computer 1 having the partial files making up the distributedfile with the particular event as a motive.

The computer 2B restores the distributed file B from the partial file B1(52) and the partial file B2 (61) thus received. Also, the computer 2Bevaluates the allocation of all the partial files making up thedistributed file based on the server information received from eachcomputer 1.

The allocation of the partial files is evaluated specifically asdescribed below. The computer 2B compares the server informationtransmitted from each computer 1 holding the partial files with theallocation rules registered in the computer 2B, and checks to seewhether the computer 1 holding the partial files of the distributed fileB complies with the allocation rules corresponding to the distributedfile B. In this embodiment, the computer 2B compares the serverinformation shown in FIG. 8 with the allocation rules shown in FIG. 6.In the case where the allocation rules are already determined for eachdistributed file, the computer 2B makes a comparison after determiningthe allocation rules corresponding to the distributed file B from theallocation rule table 23 of the computer 2B itself.

In the case where the evaluation shows the existence of the computer 1failing to comply with the allocation rules held in the computer 2B, thecomputer 2B executes the process for moving the partial files. Accordingto this embodiment, the computer 1C fails to comply with the allocationrules for the item “load”, and therefore the partial B2 (61) stored inthe computer 1C is moved. The process of moving a partial file will beexplained below.

In moving the partial files, the computer 2B first checks the number ofthe computers 1 failing to comply with the allocation rules and thenumber of the partial files stored in the computers 1 failing to complywith the allocation rules. Normally, each computer 1 stores only onepartial file, and therefore the number of the computers 1 coincides withthat of the partial files. In the presence of a computer 1 storingdouble partial files of a single distributed file, however, the numberof the partial files contained in the computers 1 is greater than thenumber of the computers 1 failing to comply with the allocation rules.The partial files thus checked make up an object of movement.

After that, the computer 2B acquires a list of the computers 1 complyingwith the allocation rules as candidates for the destination computer 1from the management computer 4. The computer 2B determines a destinationcomputer 1 from the list of the computers 1, and instructs the computer1 having the partial file making up the object of movement to move thedata to the destination computer 1.

FIG. 7 is a flowchart showing the steps of establishing the list of thecomputers 1 constituting candidate destinations.

First, the computer 2B selects all the items with the priority thereofset to 1 or higher, from the allocation rule table 23 (step 700). Afterthat, the computer 2B issues to the management computer 4 a commandmaking an inquiry about the presence or absence of the computers 1complying with the allocation rules configured of the selected items(step 701).

The management computer 4 that has received the command searches theserver information management table 44 for the computers 1 complyingwith the allocation rules made up of the received items, and transmitsthe list of the computers thus obtained to the computer 2B. In thisembodiment, the management computer 4 selects the computer 1A as acomputer 1 complying with the allocation rules of FIG. 6 and notifiesthe computer 2B (step 710).

The computer 2B that has received the list of the computers 1 complyingwith the allocation rules determines whether “load” has been selected asan item of the allocation rules held in the computer 2B (step 702). Inthe case where the item “load” is selected, the computer 2B issues acommand making inquiry about the current “load” information to all thecomputers 1 included in the received list of the computers 1. Uponreceipt of the responses from all the computers 1 to which the commandis sent, the computer 2B removes, based on the responses, the computers1 failing to meet the conditions of the item “load” from the list of thecomputers 1 acquired (step 703).

Next, the computer 2B determines whether the list includes the computers1 holding other partial files than those to be moved, which are includedin the distributed file (the distributed file B in the case underconsideration) holding the partial files to be moved. Specifically, thenames of the computers 1 storing the other partial files received fromthe management computer 4 at the time of accessing a distributed fileare compared one by one with the names of the computers 1 included inthe list. In the case where the computers 1 holding such other files areincluded in the list, the computer 2B removes the particular computers 1from the list (step 704).

Next, the computer 2B determines whether the list of the computers 1obtained in or before step 704 contains the computers 1 greater innumber than the partial files to be moved (step 705). In the case wherethe computers 1 greater in number than the partial files is contained inthe list, the computer 2B establishes the applicable allocation rulesand the list of the computers 1 (step 708). In this embodiment, theconditions of steps 702 to 705 are confirmed for the computer 1Anotified by the management computer 4, and the computer 1A is finallydetermined as a list of the destination computer 1.

In the case where the computers 1 more than the partial files to bemoved are not contained in the list of the computers 1, on the otherhand, the computer 2B removes the items lowest in priority from theallocation rule table 23 (step 706). After that, the computer 2Bdetermines whether items of 1 in priority remain in the allocation ruletable 23 as the result of removal (step 707). In the case where no itemof 1 in priority remains (all the items are removed), the computer 2Balarms the user, and determines the finally obtained list of thecomputers 1 (i.e. the list of the computers 1 before the last removal ofthe items of 1 in priority order) as a list of the destination computers1 (step 709).

In the case where the items of 1 in priority remain in the allocationrule table 23 in step 707, on the other hand, the computer 2B returns tothe process of step 701, issues a command to the management computer 4to make an inquiry about the computers 1 complying with the allocationrules configured of the remaining items, and subsequently establishes alist of the desired computers 1 by executing similar steps.

After that, the computer 2B selects at random as many destinationcomputers 1 as the partial files to be moved, from the established listof the destination computers 1. The computer 2B then transmits thepartial file IDs of the partial files to be moved the information on theprospective destination computers 1, to the computers 1 which aredetermined not to comply with the allocation rules.

The computer 1 that has received from the computer 2B the partial fileIDs of the partial files to be moved and the information on theprospective destination computers 1 specifies the storage position ofthe partial files using the partial file IDs received, and transmits thedesignated partial files to the designated computers 1.

According to this embodiment, the computer 2B selects the computer 1A asa destination computer 1, and transmits the partial file ID of thepartial file B2 (61) and the information indicating the computer 1A tothe computer 1C. The computer 1C, upon receipt of the designation,transfers the partial file B2 (61) to the computer 1A in accordance withthe designation of the computer 2B.

Assume that the list of the prospective destination computers 1 whichsatisfy the rule contains more computers 1 in number than the number ofthe partial files to be moved. Then, the computer 2B may assign aplurality of the computers as candidates of destination computers forone partial file. In this case, a plurality of partial files aredistributed so that they are assigned to one computer in a manner not todouble the distribution. After that, the computer 2B transmits aninstruction to the computers 1 storing the partial files to move thepartial files, while at the same time transmitting the informationdesignating a plurality of the computers 1 as candidate destinations.The computer 1 that has received the information on a plurality of theprospective destination computers 1 freely selects a destinationcomputer 1 using the received information on a plurality of thecomputers 1 and transfers the partial files.

Also, this embodiment can be so configured that the computer 1 havingthe partial files to be moved can hold the execution of the moveinstruction from the computer 2 until predetermined conditions are met.Further, the computer 1 holding the movement of the partial files, uponreceipt of repeated instructions to move the partial files held therein,selects, as destination computers 1, those computers 1 designated as adestination by all the move instructions.

The computer 2B, based on the process of step 709 in FIG. 7, may displayon the input/output unit an alarm to the user to the effect that thepartial files are arranged in the computers 1 failing to comply with theallocation rules and the destination computers 1 complying with theallocation rules cannot be found. Also, in the case where the list ofthe prospective destination computers 1 contains the computers 1 smallerin number than the partial files, the computer 2B may display on theinput/output unit an alarm to the user to the effect that the partialfiles are arranged in the computers 1 failing to comply with theallocation rules and the number of the destination computers 1 complyingwith the allocation rules is insufficient.

Further, the computer 2B may cause the user to determine whether a partor all of the partial files failing to comply with the allocation rulesmay be moved to the same computer 1. In the case where the users permitsthe double assignment of partial files, the computer 2B extracts thecomputers 1 at random from the list of the destination computers 1 andinstructs a plurality of the computers 1 having the partial files to bemoved, to move the partial files to the extracted computers 1.

As described above, the computers 1 may hold the execution of theprocess of moving the partial files for a predetermined length of timeor until a predetermined number of move instructions are received fromthe computer 2B. As a result, in the case where a plurality of computers2 access the same partial file during a short length of time, thephenomenon is avoided in which the partial files are moved each timethey are accessed, due to the difference of the allocation rules fromone computer 2 to another, thereby making it possible to reduce the loadotherwise imposed on the computer system by the frequent movement of thepartial files.

The computers 1 holding the process of moving the partial files executesthe moving process in the pattern described below.

First, in the case where only one process of moving the partial files isheld and only one destination computer 1 is designated as an object ofmovement, then the computers 1 holding the move process transfer thepartial files to the computers 1 designated as a destination.

In the case where only one move process is held but a plurality of thedestination computers 1 are designated as an object of movement, on theother hand, the computer 1 holding the move process selects a computer 1at random from a plurality of designated computers 1 and transfers thepartial file to the selected computer 1.

In the case where a plurality of move processes are held and one or aplurality of destination computers 1 are designated for each of the moveprocesses, then the computers 1 holding the move process transfer thepartial files to a common computer 1 among the destination computers 1designated for each process held. In the absence of a common computer 1,the computers 1 holding the move process do not execute the moveprocess.

After being notified from the destination computer 1 that the movementof the partial files is complete, the computer 2B notifies themanagement computer 4 of the partial file ID and the information(network address, etc.) on the destination computer 1 to which thepartial files are moved.

According to this embodiment, the computer 2B notifies the managementcomputer 4 of the partial file ID of the partial file B2 (61) and theinformation on the destination computer 1A to which the partial file ismoved.

The partial files may be transferred by other than the method accordingto the aforementioned embodiments.

Specifically, in the case where a plurality of computers 1 making updestinations for movement are designated, the computer 1 for executingthe move process may transfer the partial files to all the destinationcomputers 1. In this case, the partial files stored in the storage unitof the computer 1 executing the move process are deleted.

Without transferring the partial files to all the destination computers1, on the other hand, the computer 1 executing the move process mayselect a plurality of computers 1 from a plurality of candidatedestination computers 1 and transfer the partial files to the selectedcomputers 1.

Further, assume that a plurality of move processes are held eachdesignating one or a plurality of destination computers 1 and that nocommon computer 1 is available. The computer 1 holding the move processtransfers the partial files to all (or a part of) the computers 1designated as a destination for each move process.

According to this method, the computer 1 executing the move process isrequired to notify the management computer 4 that the same partial filehas been transferred to a plurality of the computers 1.

FIG. 12 is a diagram showing an example of he distributed fileinformation management table 43 held in the management computer 4according to this method. In FIG. 12, unlike in the distributed fileinformation management table 43 explained with reference to FIG. 2, aplurality of entries are prepared to be registered as information on thecomputers 1 where the partial files are held.

Also, according to this method, the advisability of arranging a partialfile in a plurality of computers 1 (hereinafter referred to as “copyinga partial file”) may be determined in the manner described below.

In a first case, the advisability is designated by the user. In thiscase, the entries shown in FIG. 13 are set as attribute information ofthe files in the distributed file information management table 43. Atthe time of creating a distributed file, the user sets the values of theentries indicated in FIG. 13 through the computer 2 thereby to determinethe advisability of copying the partial file of a given distributedfile. The computer 1 copies the partial file by referring to theinformation thus set.

In another case, advisability permission and no permission of copying apartial file is determined according to the file type, and at the timeof relocation of a distributed file, the computer 1 transferring thepartial file automatically copies the partial file based on theparticular information regarding the advisability of copying. In thiscase, the management computer 4 or the computer 1 holds the table asshown in FIG. 14 in advance.

Based on the information thus set, the computer 1 copies the partialfile. In the case where the set information is available only in themanagement computer 4, the computer 1 executing the move process makesinquiry to the management computer 4 about the advisability of copyingthe partial file, and copies the partial file in accordance with theresponse to the inquiry.

Further, according to this method, a plurality of computers 1 come tohave the same partial file. The computer 2 accessing a distributed file,therefore, is required to determine which computer 1 is to be accessedfor the partial file. Some examples of the method for this determinationare described below.

A first example is for the management computer 4 to determine thecomputer 1 to be accessed. In this case, upon receipt of an inquiry fromthe computer 2 about the location of the partial file, the managementcomputer 4 selects one computer 1 at random from a plurality oflocations registered in the partial file information management table 43and notifies the particular information to the computer 2.

In a second example, the computer 2 accessing a distributed filedetermines the computer 1 to be accessed. The management computer 4 thathas received an inquiry about the location of the partial files notifiesall the computers 2 of the information on a plurality of computers 1storing the same partial file. The computers 2 that have received theinformation on a plurality of computers 1 selects an arbitrary one ofthe plurality of the computers 1, and issues a partial file transmissionrequest. The computer 1 may be selected by the computer 2 according toany of the methods described below.

In one method, the computer 2 issues a partial file transmission requestto all the computers 1 included in the information received from themanagement computer 4, and employs the first-arriving response. In thiscase, the computer 2 transmits a partial file transmission suspensioninstruction to the other computers 1.

A second method is such that the computer 2 acquires the partial filesat the same time from all the computers 1 included in the informationreceived from the management computer 4. Specifically, the computer 2issues an acquisition request to each computer 1 by designating theoffset of each partial file (namely, a request in the wording “TransmitX bytes from the first Xth byte of the partial file” is issuedseparately to each computer 1).

This method makes it possible to relocate the partial files among thecomputers in the computer system with higher versatility.

According to the embodiments described above, the computer system, evenif a given partial file has no information on the other partial files,can arrange the partial files without any double assignment simply byacquiring the information on the computers 1 complying with theallocation rules from the management computer 4. As a result, the filescan be distributed while at the same time maintaining the security ofthe computer system.

According to this invention, the chance of concentrating all the partialfiles of a distributed file on a specific server can be avoided, and atthe same time, the distributed files can be arranged while maintainingthe security of the computer system.

Also, a plurality of various allocation rules may be laid down, and thepartial files can be arranged in versatile way accordingly.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A computer system comprising at least one first computer, a secondcomputer and a third computer, wherein said third computer hasinformation concerning said first computer, and said second computer hasinformation as an allocation rule including a plurality of evaluationitems for defining file distribution; wherein said second computer, uponreceipt of an instruction to create a distributed file, transmits saidallocation rule to said third computer; wherein said third computer,upon receipt of said allocation rule, specifies said first computercomplying with said allocation rule by reference to the informationconcerning said first computer, and transmits said informationconcerning said specified first computer to said second computer; andwherein said second computer transmits partial files of the distributedfile instructed for creation, to said first computer based on thereceived information of said first computer.
 2. A computer systemaccording to claim 1, wherein said allocation rule includes anevaluation item for the performance of said first computer.
 3. Acomputer system according to claim 1, wherein said allocation ruleincludes an evaluation item for the security of said first computer. 4.A computer system according to claim 1, wherein priority is set for eachof the evaluation items included in said allocation rule.
 5. A computersystem according to claim 1, wherein said second computer acquires theinformation concerning said first computer from said first computerhaving said partial file, and compares said allocation rule with saidacquired information on said at least one first computer to therebydetermine a relevant one of said at least one first computer failing tocomply with said allocation rule, and wherein an instruction to transfersaid partial file from said first computer failing to comply with saidallocation rule to another first computer complying with said allocationrule is transmitted to said first computer failing to comply with saidallocation rule.
 6. A computer system according to claim 5, wherein saidsecond computer acquires the information concerning said another firstcomputer complying with said allocation rule from said third computer.7. A computer system according to claim 1, wherein said first computerand said third computer are identical with each other.
 8. A computersystem according to claim 1, wherein said second computer includes aninput/output unit, and wherein said allocation rule is determined foreach file based on information input through said input/output unit. 9.A computer system according to claim 1, wherein said second computerincludes a plurality of allocation rules corresponding to file types,and uses the allocation rules corresponding to said file type for whicha creation instruction is issued.
 10. A computer connected to at leastone first computer and a second computer, comprising a control unit anda storage unit, wherein said control unit has information indicative ofallocation rules including a plurality of evaluation items for definingfile distribution, wherein said control unit transmits said allocationrules to said second computer in response to an instruction to createdistributed files, and wherein partial files of a file for which acreation instruction is given are transmitted to said second computer,based on information of said first computer received from said secondcomputer.
 11. A computer system according to claim 10, wherein saidcontrol unit acquires the information concerning said first computerfrom said first computer having said partial file, compares saidallocation rules with said acquired information on said first computerto thereby determine said first computer failing to comply with saidallocation rules, and wherein an instruction to transfer said partialfile from said first computer failing to comply with said allocationrules to said another first computer failing to satisfy said allocationrules is transmitted to said first computer failing to comply with saidallocation rules.
 12. A computer system according to claim 11, whereinsaid another computer complying with said allocation rules is determinedwhile removing said first computer having said other partial filesrelated with said first partial file.
 13. A method of file distributionfor a computer system including first computers, a second computer and athird computer, said second computer having information as an allocationrule including a plurality of evaluation items for defining distributionof files, said method comprising the steps of: transmitting saidallocation rule to said third computer from said second computer whensaid second computer is instructed to create a distributed file; andspecifying a relevant one of said first computers meeting saidallocation rule, through said third computer that has received saidallocation rule, with reference to information concerning said firstcomputers, and transmitting information concerning said specified firstcomputer to said second computer; said second computer transmittingpartial files of a file instructed for creation, to said relevant firstcomputer based on said received information concerning said firstcomputer.
 14. A method of file distribution according to claim 13,wherein said second computer acquires the information on said firstcomputer from said first computer having said partial file, comparessaid allocation rule with said acquired information on said firstcomputer to thereby determine a particular one of said first computersfailing to satisfy said allocation rule, and instructs said particularfirst computers failing to satisfy said allocation rule to transfer saidpartial files from said particular first computer failing to comply withsaid allocation rule to said other first computer satisfy saidallocation rule.